This invention relates to liquid cleaning concentrates and more particularly to concentrates suitable for formulating alkali cleaning compositions having utility in the food industry.
The use of caustic solutions to wash glassware, such as bottles and other food and beverage containers, is widespread in the industry. In fact, the use of caustic solutions is generally controlled by law or by industry requirements. For example, regulations require dairies, soft drink plants and breweries to maintain a specified caustic concentration in their bottle washers. Generally, solid compositions are employed which are diluted in the plant prior to use in the cleaning equipment.
Thus, for example, U.S. Pat. No. 2,976,248 discloses a solid bottle washing composition containing 70-99 percent caustic, a sequesterant which may be gluconic acid and a potassium or sodium lignosulfonate, the latter component functioning as a corrosion-inhibiting agent. The aqueous solutions of these compositions contain from about 1 to 10 percent by weight of caustic. U.S. Pat. No. 2,584,017 discloses a solid composition containing both sodium hydroxide and sodium carbonate, sodium gluconate and wetting agent while U.S. Pat. No. 3,312,624 discloses formulations containing between 88-99 percent by weight of caustic and from 1 to 12 percent by weight of a particular surfactant blend.
Alkali based solid cleaning compositions for other uses have also been described in the prior art. For example, U.S. Pat. No. 3,583,923 describes a multi-component heavy duty cleaning composition which includes from about 35 to about 50 parts by weight of an alkali metal hydroxide. An oven cleaner containing 1.0 to 20 parts alkali metal hydroxide, gluconic acid and numerous other ingredients is described in U.S. Pat. No. 3,644,210.
While cleaning solutions prepared from such solid compositions have utility in various applications, the preparations of both the solid composition and the aqueous solution present difficulties. Thus, solid compositions containing sodium hydroxide are difficult to prepare, requiring careful handling and expensive equipment. Typical are the teachings of U.S. Pat. Nos. 2,767,146 and 2,804,432. The former patent teaches a composition containing gluconic acid and sodium hydroxide made by spraying gluconic acid solution upon powdered, flake or granular sodium hydroxide. It is taught that the problem of forming particles of this character is aggravated by the excessive heat created by the exothermic reaction of gluconic acid with sodium hydroxide. Special equipment and/or techniques are taught to obviate this difficulty. U.S. Pat. No. 2,804,432 teaches a process for making similar particles by adding gluconic acids in aqueous solution to a hot supersaturated aqueous solution of the caustic, mixing the two solutions together while cooling the mixture until solid non-adherent particles are formed. Again, critical processing variables are involved in order to obtain the desired product.
In addition to being difficult to formulate, solid compositions containing large amounts of caustic are hazardous to ship and present problems in the customer's plant. Thus, the desired cleaning solution must be made on site using these solid pellets. Accordingly, dilute caustic solutions have been proposed in the art. Thus, U.S. Pat. No. 3,653,095 describes an alkaline solution containing up to 10 percent alkali, alkyl glycoside and a selected metal ion in combination with certain surface active agents. The compositions are taught to protect substrates such as aluminum, zinc, tin, lead, alloys thereof and siliceous compositions from attack by the alkaline solution. Although dilute alkaline solutions obviate the processing, storage and handling problems inherent in solid compositions, they are subject to severe economic disadvantages in that large quantities of water must be shipped to the customer.
While the preparation of liquid compositions containing reasonably concentrated amounts of alkali has been a desirable objective, the solution problems inherent in working with concentrated caustic solutions have heretofore presented problems. Thus, in TRITON BG-5, Technical Bulletin of Rohm and Haas Company, Philadelphia, Pa., June 1968, it is taught that up to 1% by weight of a nonionic surfactant and an alkoxylated glycidyl ether can be solubilized in 50% sodium hydroxide solution. U.S. Pat. No. 3,437,598 discloses aqueous concentrates comprising 40% to 70% caustic soda and between about 0.005% to 1% of a water-soluble adduct of glycidol and an alkylphenol.